Piezoelectric actuator for haptic device

ABSTRACT

A haptic device includes a flexible holder; an elongated piezo bender supported at one end thereof by the holder; a mass supported by the elongated piezo bender and positioned at an end of the elongated piezo bender opposite the end supported by the holder; and an electrical driving signal generator configured to generate a signal to create a vibration in the elongated piezo bender.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalPatent Application No. 61/562,199, filed Nov. 21, 2011, the entirecontent of which is incorporated herein by reference.

FIELD

The present invention is related to piezoelectric actuators for hapticdevices.

BACKGROUND

Electronic device manufacturers strive to produce a rich interface forusers. Conventional electronic devices often provide visual and/orauditory feedback to communicate information to users. In some cases,kinesthetic feedback (such as active and resistive force feedback)and/or tactile feedback (such as vibration, texture, and heat) may alsobe provided to the user to enhance the user experience. Generallyspeaking, kinesthetic feedback and tactile feedback are collectivelyknown as “haptic feedback” or “haptic effects.” Haptic feedback may beuseful for providing cues to alert the user of specific events or toprovide realistic feedback sensations to create a greater sensoryexperience. Haptic feedback can be used with common electronic devicesand even devices used for creating a simulated or virtual environment.

Various haptic actuation technologies have been used in the past toprovide vibrotactile haptic feedback to touch sensitive devices, such astouch screens. Known haptic feedback devices use electric actuators,such as Linear Resonant Actuator (“LRA”) devices and Eccentric RotatingMass (“ERM”) devices. However, these actuators usually have very limitedbandwidth to perform sufficiently in haptic applications.

Another conventional haptic feedback technology in touch sensitivedevices is electro-active polymer (“EAP”) devices. One drawback of thistechnology, however, is that EAP-based actuators normally requirethousands of volts of electricity to provide effects that are suitablefor haptic applications.

Development of haptic feedback structures has led to smaller, morecompact devices. As display screens having high definition haveincreased, so has the need for high definition haptic feedback.

SUMMARY

According to an aspect of embodiments of the present invention, there isprovided a haptic device that includes a flexible holder, an elongatedpiezo bender supported at one end thereof by the holder, a masssupported by the elongated piezo bender and positioned at an end of theelongated piezo bender opposite the end supported by the holder, and anelectrical driving signal generator configured to generate a signal tocreate a vibration in the elongated piezo bender.

BRIEF DESCRIPTION OF THE DRAWINGS

The components of the following figures are illustrated to emphasize thegeneral principles of the present disclosure and are not necessarilydrawn to scale. Reference characters designating correspondingcomponents are repeated as necessary throughout the figures for the sakeof consistency and clarity.

FIG. 1 is a block diagram showing a general schematic of an electronicdevice, according to embodiments of the invention;

FIG. 2 is a schematic cross-sectional view of a haptic device accordingto an embodiment of the invention;

FIG. 3 is a schematic view of a portion of the haptic device of FIG. 2;

FIG. 4 is an exploded view of an actuator portion of the haptic deviceof FIG. 2; and

FIG. 5 is a schematic side view of an embodiment of the actuator of FIG.4.

DETAILED DESCRIPTION

The present disclosure describes embodiments of haptic devices thatinclude haptic feedback actuators that impose haptic effects on a uservia a user interface, human-computer interface, or other portions of auser device on which or within which the actuators reside. Inparticular, the embodiments of the haptic devices described herein canbe configured to apply haptic effects to a touch sensitive surface of auser device. The touch sensitive surface, in some embodiments, can bepart of a display device that may include both a visual output mechanismand a touch sensitive input mechanism. Thus, haptic feedback can beapplied in user devices, such as electronic handheld devices, forproviding a rich sensory experience for the user.

Although many of the examples described herein relate to touch screendevices, it should be understood that the present disclosure alsoencompasses other types of human-computer interfaces involving touchsensitive structures. In addition, other features and advantages will beapparent to one of ordinary skill in the art upon reading andunderstanding the general principles of the present disclosure. Theseother features and advantages are intended to be included in the presentdisclosure as well.

FIG. 1 is a block diagram of an electronic device 10 in accordance withone embodiment. More particularly, the electronic device 10 includes aprocessing device 12, a memory device 14, and input/output devices 16,which are interconnected via a bus 18. Furthermore, the input/outputdevices 16 include a touch screen device 20 or other human-computerinterface devices.

The touch screen device 20 may be configured as any suitablehuman-computer interface or touch/contact surface assembly. The touchscreen device 20 may be any touch screen, touch pad, touch sensitivestructure, computer monitor, laptop display device, workbook displaydevice, kiosk screen, portable electronic device screen, or othersuitable touch sensitive device. The touch screen device 20 may beconfigured for physical interaction with a user-controlled device, suchas a stylus, finger, etc. In some embodiments, the touch screen device20 may include at least one output device and at least one input device.For example, the touch screen device 20 might include a visual displayand a touch sensitive screen superimposed thereon to receive inputs froma user's finger. The visual display may include a high definitiondisplay screen.

In various embodiments, the touch screen device 20 provides hapticfeedback to at least a portion of the electronic device 10, which can beconveyed to a user in contact with the electronic device 10.Particularly, the touch screen device 20 can provide haptic feedback tothe touch screen itself to impose a haptic effect when the user in iscontact with the screen. The haptic effects can be used to enhance theuser experience, and particularly can provide a confirmation to the userthat the user has made sufficient contact with the screen to be detectedby the touch screen device 20.

The electronic device 10 may be any device, such as a desk top computer,laptop computer, electronic workbook, electronic handheld device (suchas a mobile phone, gaming device, personal digital assistant (“PDA”),portable e-mail device, portable Internet access device, calculator,etc.), kiosk (such as an automated teller machine, ticking purchasingmachine, etc.), printer, point-of-sale device, game controller, or otherelectronic device.

The processing device 12 may be a general-purpose or specific-purposeprocessor or microcontroller for managing or controlling the operationsand functions of the electronic device 10. For example, the processingdevice 12 may be specifically designed as an application-specificintegrated circuit (“ASIC”) to control output signals to a driver of theinput/output devices 16 to provide haptic effects. The processing device12 may be configured to decide, based on predefined factors, what hapticeffects are to be played, the order in which the haptic effects areplayed, and the magnitude, frequency, duration, and/or other parametersof the haptic effects. The processing device 12 can also be configuredto provide streaming motor commands that can be used to drive the hapticactuators for providing a particular haptic effect. In some embodiments,the processing device 12 may actually include a plurality of processors,each configured to perform certain functions within the electronicdevice 10.

The memory device 14 may include one or more internally fixed storageunits, removable storage units, and/or remotely accessible storageunits. The various storage units may include any combination of volatilememory and non-volatile memory. The storage units may be configured tostore any combination of information, data, instructions, software code,etc. More particularly, the storage devices may include haptic effectprofiles, instructions for how the haptic actuation devices of theinput/output devices 16 are to be driven, or other information forgenerating haptic effects.

In addition to the touch screen device 20, the input/output devices 16may also include specific input mechanisms and output mechanisms. Forexample, the input mechanisms may include such devices as keyboards,keypads, cursor control devices (e.g., computer mice), or other dataentry devices. Output mechanisms may include a computer monitor, virtualreality display device, audio output device, printer, or otherperipheral devices. The input/output devices 16 may include mechanismsthat are designed to not only receive input from a user and but alsoprovide feedback to the user, such as many examples of touch screendevices. The touch screen device 20 and other input/out devices 16 mayinclude any suitable combination and configuration of buttons, keypads,cursor control devices, touch screen components, stylus-receptivecomponents, or other data entry components. The touch screen device 20may also include any suitable combination of computer monitors, displayscreens, touch screen displays, haptic or tactile actuators, hapticeffect devices, or other notification devices for providing output tothe user.

FIG. 2 illustrates an embodiment of a haptic device 100 that may be usedas part of the input/output devices 16 of FIG. 1. As illustrated, thehaptic device 100 includes an actuator 102 that includes a piezo bender110 having a thin elongated body that is supported at or near one end bya holder 120 that is configured to hold the piezo bender 110 in a mannerthat restrains movement of the portion of the piezo bender 110 beingheld. Piezo benders are known in the art and generally include at leastone layer of piezo ceramic material and at least one layer of a metalsubstrate. A mass 130 is attached to an end of the piezo bender 110 thatis opposite the holder 120. As illustrated in FIG. 2, the piezo bender110 may be connected to an electrical driving circuit 140 that isconfigured to generate an electrical driving signal based on an inputsignal. When the electrical driving signal is applied to the piezobender 110 across two surfaces of the piezo bender 110, the piezo bender110 will begin to deflect. By varying the frequency of the electricaldriving signal, the piezo bender 110 will vibrate. The frequency andamplitude of the driving signal provided by the driving circuit 140, thenatural mechanical resonant frequency of the piezo bender 110, thelength of the piezo bender, and the size of the mass 130 will controlthe frequency and amplitude of the vibration of the piezo bender 110 andhaptic effect provided by the haptic device. The mass 130 may beconnected to the piezo bender 110 by any suitable means, such as with anadhesive.

When the proper voltage is applied to the piezo bender 110, the piezobender 110 will bend from the fixed end, moving the mass 130 back andforth. The motion of the mass 130 provides acceleration to the attachedsystem. By varying the length of the cantilever distance l and the sizeof the attached mass 130, both frequency and acceleration may becontrolled. In an embodiment, the center of gravity of the mass 130 maybe positioned as far as possible from the holder 120, while stillfitting in the space constraints of the haptic device 100.

As illustrated in FIG. 3, if it is assumed that the holder 120 is anideal fixed clamp at one end of the piezo bender 110 and the mass 130 isfirmly attached at the other end of the piezo bender 110, the system isgoverned by the following equations:

$\begin{matrix}{\omega = {{2\;\pi\; f} = \sqrt{\frac{K}{m}}}} & (1) \\{K = \frac{C_{f}{EI}}{L^{3}}} & (2)\end{matrix}$where ω is the resonant frequency of the system, K is the stiffness ofthe system, and m (in kg) is the floating mass 130 attached to the piezobender 110 plus the mass of the piezo bender 110 itself. In equation(2), L (in meters) is the distance cantilevered from the holder 120providing the fixed mount, and C_(f) is a clamping factor that can rangefrom 0 to 3 for the cantilever configuration illustrated in FIG. 3. Aclamping factor C_(f) of 3 indicates a perfectly stiff holder, while alower value represents a holder with some compliance, i.e., a flexibleholder. Further, EI in equation (2), which is an actuator modulus, maybe calculated for a particular piezo bender using a cantilevered beamfixture to measure static free displacement D and blocking force F:

$\begin{matrix}{{EI} = \frac{{Fl}^{3}}{3\; D}} & (3)\end{matrix}$where F in equation (3) is the force of the piezo bender, l is thelength of piezo bender 110 minus a length of the piezo bender that isclamped in the holder 120, for example, 3 mm, and D is the static freedisplacement, as illustrated in FIG. 3.

Combining equations (1)-(3) above for modulus (EI), beam stiffness (K),and resonant frequency (ω) yields a single equation (4) that may be usedto describe the actuator system:

$\begin{matrix}{\omega = {{2\;\pi\; f} = \sqrt{\frac{C_{f}{Fl}^{3}}{3\; m\;\Delta\; L^{3}}}}} & (4)\end{matrix}$It is possible to predict a resonant frequency based on a particularpiezo actuator's performance and moving mass by using equation (4).

The clamping factor C_(f) may be controlled through the use of epoxiesand/or mechanical means. As noted above, the clamping factor C_(f) canrange from 0 (totally loose) to 3 (traditional hard mount). By using aflexible holder (mount) through the use of epoxy and/or mechanicalmeans, the clamping factor C_(f) may be reduced to between about 1 andabout 2, and desirably between about 1 and about 1.5. By lowering theclamping factor C_(f), the overall resonant frequency may be lowered toa range that is acceptable to use in the haptic device 100.

FIG. 4 illustrates an embodiment of the actuator 102 illustrated in FIG.2. As illustrated, the holder 120 includes a structure 122, which may bemolded from a plastic material, that may be part of a housing of theelectronic device 10 described above, or may be a separate structurethat may be attached to the housing. In an embodiment, the holder 120may also include an epoxy 124 or some other resin that may be used toattach the piezo bender 110 to the structure 122. The actuator 102 mayinclude a top cover 150 a and a bottom cover 150 b that surround andprotect the piezo bender 110 and the mass 130.

FIG. 5 illustrates an embodiment of the actuator 102 of FIG. 4 with theaddition of hard stops 160 and soft stops 162 that may be placed atspecific locations around the piezo bender 110 and the mass 130. Theterms “hard” and “soft” are relative terms meant to describe materialshaving different hardness values, as understood by one of skill in theart. The hard stops 160 and the soft stops 162 are configured to allowthe piezo bender 110 and the mass 130 to be minimally constrained andperform normally when the voltage is applied to the piezo bender 110,yet protect the piezo bender 110 and the mass 130 from highaccelerations that are generated if the haptic device 100 isaccidentally dropped. More or less hard stops 160 and soft stops 162 maybe used. The illustrated embodiment is not intended to be limiting inany way.

In alternative embodiments, other shapes for the piezo-based actuatorsmay be used. The illustrated embodiments are not intended to be limitingin any way. In addition, the piezo materials, described herein may bereplaced with other smart materials that are used in actuators, such asa shape memory alloy (“SMA”). In an embodiment, the piezo-basedactuators may also be configured to be sensors to sense an input from auser of the electronic device. Aspects of embodiments of the presentinvention may be used in other actuators, and not just for the resonantactuators of the haptic devices disclosed herein. In addition, aspectsof embodiments of the present invention may provide an improved level ofcompatibility and performance, as compared to haptic devices known inthe art, which may be suitable for high definition devices.

Embodiments of the present invention may be used as the actuation unitto enable haptic feedback in various electronic devices, such as touchscreen handheld devices (mobile devices, PDA, and navigation systems),automotive applications, gaming consoles, etc.

The embodiments described herein represent a number of possibleimplementations and examples and are not intended to necessarily limitthe present disclosure to any specific embodiments. Instead, variousmodifications can be made to these embodiments as would be understood byone of ordinary skill in the art. Any such modifications are intended tobe included within the spirit and scope of the present disclosure andprotected by the following claims.

What is claimed is:
 1. A haptic device, comprising: a flexible holder;an elongated piezo bender supported at one end thereof by the holder; amass supported by the elongated piezo bender and positioned at an end ofthe elongated piezo bender opposite the end supported by the holder; andan electrical driving signal generator configured to generate a signalto create a vibration in the elongated piezo bender.
 2. The hapticdevice according to claim 1, wherein the flexible holder comprises astructure and an epoxy material configured to attach the elongated piezobender to the structure.
 3. The haptic device according to claim 1,wherein a clamping factor provided by the flexible holder is betweenabout 1 and about
 3. 4. The haptic device according to claim 3, whereinthe clamping factor is between about 1 and about
 2. 5. The haptic deviceaccording to claim 4, wherein the clamping factor is between about 1 andabout 1.5.
 6. The haptic device according to claim 1, further comprisinga cover configured to cover the elongated piezo bender and the mass. 7.The haptic device according to claim 6, further comprising a stoppositioned between the cover and the elongated piezo bender.
 8. Thehaptic device according to claim 6, further comprising a stop positionedbetween the cover and the mass.